Turbine blades are the primary elements of wind turbines for converting wind energy into electrical energy. The turbine blades typically consist of a suction side shell member and a pressure side shell member that are bonded together at bond lines along the trailing and leading edges of the blade. The bond lines are generally formed by applying a suitable bonding paste or compound along the bond line at a minimum designed bond width between the shell members.
Inevitably, defects occur in the blades from the original manufacturing process or as a result of operational conditions experienced by the blade. For instance, a void in the original bonding material (i.e., from an air bubble or lack of complete fill) may eventually initiate delamination of the blade materials. Impact damage from ice, hail, lightning, birds, etc., often results in delamination. Thermal cycling (e.g., between winter and summer temperatures) may also result in blade damage. Water penetration through a crack in the external gel coat can also lead to delamination. The delamination may exist between the shell members (e.g., within the bonding material) or interlaminate (within the shell member layers).
The blade defects must be repaired, typically at the site, to ensure efficient operation of the wind turbine at over its design life and power rating. The conventional repair procedures for subsurface defects in the blade laminate call for grinding of the effected blade area and subsequent reapplication of the laminate materials. A defect is removed by grinding/sanding the laminate plies until the defect is exposed. The laminate layers are then reapplied and sanded smooth. Typically, an “over-laminate” ply is added to the repair area for additional strength. However, this additional laminate layer extends above the planar surface of the surrounding blade area and thus disrupts airflow over the blade and degrades aerodynamic performance. In addition, the grind/over-laminate repair procedure requires extensive surface preparation and skill to apply the repair laminate materials, followed by sanding, over-laminating, and painting, all of which are quite laborious and time consuming (e.g., a 2-3 day process).
A “drill and fill” technique has been used to repair blade defects in newly manufactured blades (before the blades are deployed in the field). This procedure involves drilling a hole into the defect void and subsequently filling the void with a bonding material. This procedure has not been considered useful for field repairs because of the likelihood of the defect being contaminated with dirt and oxides, resulting in inconsistent repair results. In addition, the structural strength of the repair is not optimal.
Accordingly, the industry would benefit from an improved repair procedure for wind turbine blades that is less time consuming, particularly suited for on-site repairs, and results in consistent and structurally sound repairs.